The invention relates to a process for the heat treatment of cylindrical bodies, in particular pipes, in particular of ceramic material, which are transported in horizontal position during the heat treatment through various temperature zones and are turned about their own axes at least on that part of the transportation route with the highest temperature.
The invention furthermore relates to an installation for the implementation of such a process, consisting of several, successively arranged chambers having heating devices and transportation means for the transportation of the cylindrical bodies in horizontal position through the chambers.
It is known to heat-treat ceramic pipes in a continuous furnace (European Patent Application No. 0,005,940). The furnace is subdivided into three zones, namely into a preheating zone, a main heating and sintering zone and into a cooling zone. Through the first zone, the pipes are supported on carriers whilst they are transported and dried. In the second zone, in which the ceramic material of the pipes becomes thermoplastic, the pipes are rolled along the floor of the furnace in order both that they are heated evenly over their circumference and that cross-sectional deformation is prevented. In the last zone, the pipes are again borne by supports whilst being transported and cooled.
The heat treatment of the pipes in such furnaces is unfavorable for various reasons. Since heating of the pipes is essentially performed from outside by means of heat radiation from the furance roof and walls of the furnace, but the heat conduction of the pipe wall is poor in the case of most ceramic materials, it takes a relatively long time before the pipes have been brought to the desired temperature right through to the inside. Long treatment times require long furnaces and are therefore unfavorable from heat economy aspects. If it were attempted to roll the pipes along the entire transportation route in order to obtain an even heating or an even cooling over the entire circumference from the outset, there would be the danger that the pipes become axially offset on the furnace floor and run into the walls. Furthermore, in this case the transportation rate would depend on the rotational speed on which even heating directly depends and, thus, with a prescribed duration of stay in the individual zone, determine the length of the treatment zone.